在WinForms上使用TPL進行並行編程

Question

我試圖在WinForms .NET 4.0上使用TPL，我按照這些步驟（轉到文章末尾）為WPF做了一些小改動，因此它可以在WinForms上工作，但它仍然無法工作..它應該顯示標簽和richTextBox上的結果，但它不...我認為並行處理工作導致鼠標開始移動緩慢一段時間我點擊按鈕..

public static double SumRootN(int root)
{   double result = 0;
    for (int i = 1; i < 10000000; i++)
    {   result += Math.Exp(Math.Log(i) / root);}
    return result;
}
private void button1_Click(object sender, EventArgs e)
{   richTextBox1.Text = "";
    label1.Text = "Milliseconds: ";
    var watch = Stopwatch.StartNew();
    List<Task> tasks = new List<Task>();
    for (int i = 2; i < 20; i++)
    {   int j = i;
        var t = Task.Factory.StartNew
          (   () =>
                {   var result = SumRootN(j);
                    Dispatcher.CurrentDispatcher.BeginInvoke
                        (new Action
                             (   () => richTextBox1.Text += "root " + j.ToString() 
                                   + " " + result.ToString() + Environment.NewLine
                             )
                         , null
                        );
                 }
            );
        tasks.Add(t);
    }
    Task.Factory.ContinueWhenAll
         (  tasks.ToArray()
            , result =>
                {   var time = watch.ElapsedMilliseconds;
                    Dispatcher.CurrentDispatcher.BeginInvoke
                          (   new Action
                                (    () =>
                                      label1.Text += time.ToString()
                                 )
                           );
                }
        );
}

Answer 1

您的代碼將無法正常工作，因為顯示結果的線程UI與WPF完全不同。 使用WPF，線程UI是Dispatcher，但在Windows Form上是另一個。

我修改了你的代碼以幫助它工作。

    private void button1_Click(object sender, EventArgs e)
    {
        richTextBox1.Text = "";
        label1.Text = "Milliseconds: ";

        var watch = Stopwatch.StartNew();
        List<Task> tasks = new List<Task>();
        for (int i = 2; i < 20; i++)
        {
            int j = i;
            var t = Task.Factory.StartNew(() =>
            {
                var result = SumRootN(j);
                richTextBox1.Invoke(new Action(
                        () =>
                        richTextBox1.Text += "root " + j.ToString() + " " 
                              + result.ToString() + Environment.NewLine));
            });
            tasks.Add(t);
        }

        Task.Factory.ContinueWhenAll(tasks.ToArray(),
              result =>
              {
                  var time = watch.ElapsedMilliseconds;
                  label1.Invoke(new Action(() => label1.Text += time.ToString()));
              });
    }

Answer 2

暫且不談這樣做是否合適，從學習角度並在評論主題“System.Windows.Threading.Dispatcher和WinForms？”中提到。 有點混亂的答案 ：

“如果您確定要在UI線程中（例如，在一個button.Click處理程序中），Dispatcher.CurrentDispatcher將為您提供UI線程調度程序，您可以像往常一樣從后台線程調度到UI線程”

有必要提一下（ 也提供了我對上述問題的回答）：

• Task.Factory.StartNew()在與主UI或其子線程不同的多個線程上生成執行
• 可以在任何線程上使用Dispatcher
• WPF應用程序OOTB（Out-of-thebox）提供Winfows表單中缺少UI線程的System.Windows.Threading.Dispatcher DispatcherObject.Dispatcher
• 問題使用Dispatcher.CurrentDispatcher正在通過任務非ui線程生成調度程序

無論如何，從對原始WPF代碼進行最小更改的教學觀點來看，您應該已經捕獲並使用了UI調度程序：

private void button1_Click(object sender, EventArgs e)
{   Dispatcher dispatcherUI = Dispatcher.CurrentDispatcher;//added **********
    richTextBox1.Text = "";
    label1.Text = "Milliseconds: ";
    var watch = Stopwatch.StartNew();
    List<Task> tasks = new List<Task>();
    for (int i = 2; i < 20; i++)
    {   int j = i;
        var t = Task.Factory.StartNew
          (   () =>
                {   var result = SumRootN(j);
      //Dispatcher.CurrentDispatcher.BeginInvoke//***changed to
                    dispatcherUI.BeginInvoke
                        (new Action
                             (   () => richTextBox1.Text += "root " + j.ToString() 
                                   + " " + result.ToString() + Environment.NewLine
                             )
                         , null
                        );
                 }
            );
        tasks.Add(t);
    }
    Task.Factory.ContinueWhenAll
         (  tasks.ToArray()
            , result =>
                {   var time = watch.ElapsedMilliseconds;
     //Dispatcher.CurrentDispatcher.BeginInvoke//**************changed to
                    dispatcherUI.BeginInvoke//added
                          (   new Action
                                (    () =>
                                      label1.Text += time.ToString()
                                 )
                           );
                }
        );
} 

Answer 3

如下面的鏈接所述，正確的方法是完全消除Dispatcher類的使用。相反，您應該創建TaskScheduler的相關實例並將其傳遞給Task方法。 http://blogs.msdn.com/b/csharpfaq/archive/2010/06/18/parallel-programming-task-schedulers-and-synchronization-context.aspx

那是

Task.Factory.ContinueWhenAll(tasks.ToArray(),
      result =>
      {
          var time = watch.ElapsedMilliseconds;
          this.Dispatcher.BeginInvoke(new Action(() =>
              label1.Content += time.ToString()));
      });

會成為

var ui = TaskScheduler.FromCurrentSynchronizationContext();
Task.Factory.ContinueWhenAll(tasks.ToArray(),
    result =>
    {
        var time = watch.ElapsedMilliseconds;
        label1.Content += time.ToString();
    }, CancellationToken.None, TaskContinuationOptions.None, ui);